The ACLS algorithm refers to the set of systematic clinical decision trees published by the American Heart Association (AHA) that guide healthcare providers through life-threatening cardiac emergencies. There are 6 core ACLS algorithms: the Cardiac Arrest Algorithm (covering VF/pVT and PEA/Asystole), the Bradycardia Algorithm, the Tachycardia Algorithm (stable and unstable), the Post-Cardiac Arrest Care Algorithm, and the Acute Coronary Syndrome Algorithm. Mastering these algorithms is required for ACLS certification and is directly tested in the certification exam. This guide breaks down each algorithm step by step with the 2026–2026 AHA guidelines.
The cardiac arrest algorithm is the most important ACLS pathway. It begins when a patient is unresponsive with no normal breathing and no pulse. The first step is always to activate the emergency response and begin high-quality CPR.
Step 1 — Confirm arrest and begin CPR: Immediately begin chest compressions at a rate of 100–120 per minute with a depth of at least 2 inches. Minimize interruptions — CPR quality is the single most important determinant of survival. Attach defibrillator/monitor as soon as available.
Step 2 — Analyze rhythm (every 2 minutes): The algorithm splits into 2 pathways based on rhythm:
Medications in cardiac arrest:
Airway management: Basic airway (BVM) is acceptable during CPR. Advanced airway (supraglottic or endotracheal intubation) should not interrupt compressions. Once advanced airway is placed, deliver 1 breath every 6 seconds (10 breaths/minute) with continuous compressions.
Bradycardia is defined as a heart rate less than 60 beats per minute. The ACLS bradycardia algorithm applies when the heart rate is below 50 bpm AND the patient shows signs of hemodynamic compromise (unstable bradycardia).
Signs of unstable bradycardia (the 4 Hs):
Stable bradycardia: If the patient is alert, normotensive, and comfortable — even with a rate below 50 — ACLS intervention may not be needed. Monitor and evaluate the cause. Stable bradycardia due to beta-blocker overdose, calcium channel blocker toxicity, or hypothyroidism is managed differently from primary cardiac causes.
Treatment sequence for unstable bradycardia:
Tachycardia in the ACLS context means heart rate greater than 150 bpm causing symptoms. The algorithm first assesses stability.
Unstable tachycardia (any type): If the patient has hypotension, altered mental status, chest pain, or acute pulmonary edema — perform immediate synchronized cardioversion. Sedate first if conscious. Starting energy: narrow regular 50–100J, narrow irregular 120–200J, wide regular 100J, wide irregular (VF treatment protocol).
Stable narrow-complex tachycardia (QRS < 0.12 sec):
Most commonly SVT (supraventricular tachycardia).
Stable wide-complex tachycardia (QRS > 0.12 sec):
Assume ventricular tachycardia until proven otherwise.
The H's and T's are the 10 reversible causes of cardiac arrest that must be identified and treated during the resuscitation effort. Treating reversible causes is especially important in PEA and asystole, where no shockable rhythm exists and the underlying cause is the only path to return of spontaneous circulation (ROSC).
The H's:
The T's:
After return of spontaneous circulation (ROSC), the post-cardiac arrest care algorithm begins. This phase is critical — most deaths after successful resuscitation occur in the first 24 hours due to hemodynamic instability, anoxic brain injury, and organ failure.
Immediate priorities after ROSC:
Prepare for your ACLS certification with our ACLS Advanced Cardiovascular Life Support study guide and our ACLS video questions and answers to test your algorithm knowledge. You can also take our full ACLS practice test to assess your readiness before the certification exam.